The present invention relates to a voltage converter and an electric drive system comprising a voltage converter and a method for reducing interference voltages. In particular, the present invention relates to the reduction of interference voltages from a voltage converter.
The German patent application DE 41 07 391 A1 discloses an electric vehicle comprising a battery-fed inverter, in particular comprising a pulse-controlled inverter. A three-phase traction motor of an electric vehicle is fed in this case via an inverter. The inverter draws its energy from a battery.
Pulse-controlled inverters can cause common-mode interference in the event of a capacitive loading such as occurs, for example, as a result of stray capacitances in a connected electric machine. In this case, it is desirable to reduce the interference voltage spectrum emitted in the environment of an electric machine in order for example to improve radio reception, in particular in the medium-wave frequency range. Besides active filter techniques it is known in this case, for example, to integrate a common-mode inductor into the connecting line between pulse-controlled inverter and electric machine. Since the connected electric machines are generally polyphase machines, such a common-mode inductor must comprise all the connecting lines.
Also known are filter structures that partly reduce the coupling-out of interference on account of power electronic switching processes via the electric motor. Interference currents and interference voltages arise as a result of parasitic capacitances from the motor windings to the motor housing and to the motor rotor. In this case, the filter structures have a positive effect, on the one hand, since the interference voltage at the rotor (vehicle shaft, MW interference in the motor vehicle) is reduced, and a negative effect, on the other hand, since the parasitic capacitance between the motor windings and the stator (housing) is increased on account of the additionally incorporated filter capacitor. As a result, the undesired interference currents are increased further. This has a disadvantageous effect in terms of e.g. magnetic field emissions and interference voltages or currents on the HV-DC supply lines.
On account of the increasing importance of electric vehicles there is therefore a need for a voltage converter which enables an effective and at the same time cost-effective filtering of interference voltages. In this case, the intention is to reduce the outlay for the filter components, to enable a delimitation of the filter effect with regard to frequency range, to limit the current through the inserted capacitors, to damp filter resonance points and additionally to reduce negative effects on other emission problems and measuring methods.